Optus this week launched an IOU feature on its prepaid mobile plans, in effect giving you emergency access if your credit runs out and you can’t find somewhere to top it up (or you’re waiting until pay day). Text IOU to 468 and you get $3 of credit, which is automatically deducted from the value of your next top-up. That could potentially be helpful, but note the fine print: you need to top up within three days or you’ll lose the value of the credit, while still being charged for it. Also, you can’t use the option until your balance dips below $1.50. Rates remain the same as your existing plan, so if you really do need that $3 to survive until Friday, spend it on texts for maximum value.